Field of the Invention
The present invention relates to a method for controlling the quality of a production of tyres. The present invention also relates to a plant for producing tyres.
Description of the Related Art
Tyre production cycles provide for obtaining and/or assembling the various components of a tyre being processed in one or more building lines and then subjecting the tyre being processed to a moulding and vulcanisation process adapted to define the structure of the tyre according to a desired geometry and tread pattern.
In order to obtain the components of the tyre, starting components are provided, from which semifinished products are obtained.
Then, a green tyre is built starting from one or more semifinished products, and the green tyre is moulded and vulcanised.
The moulded and vulcanised tyre is subjected to a manual visual control after which it can be discarded or catalogued as acceptable and hence intended for the market (for the first set-up or for “replacement” parts).
Possible modifications to the production process for correcting flaws are entrusted to the experience of the operator who controls the discard, based on the type and size of the tyre.
With the term “starting components” it is intended one or more from among elastomeric materials and cords comprising at least one textile and/or metal thread employed for building a tyre. The set of multiple threads preferably has the threads twisted together.
With the term “elastomeric material” it is intended to indicate a composition comprising at least one elastomeric polymer and at least one reinforcement filler. Preferably, such composition also comprises additives such as a cross-linking agent and/or a plasticisation agent. Due to the presence of the cross-linking agent, such material can be cross-linked by means of heating, so as to form the final manufactured product.
With the term “green tyre” a tyre is indicated that is obtained at the end of the building process and not yet moulded and vulcanised.
With the term “tyre being processed” it is intended the set of one or more parts of the green tyre built on a forming support, comprising the starting components, the green tyre and the moulded and vulcanised tyre to be subjected to control.
With the term “semifinished product” it is intended a semifinished product of piece or cut-to-size conventional type such as a liner, under-liner, anti-abrasive elongated element, complex (the set including liner, under-liner and anti-abrasive elongated element), bead core, bead core filler, reinforcement insert, sidewall insert, sidewall, carcass ply, belt layer, under-layer, tread band, etc., or to an “elementary” semifinished product, i.e. in the form of at least one of the following: a continuous elongated element made of elastomeric material; a textile and/or metal reinforcement cord preferably covered with elastomeric material; a band-like element made of elastomeric material comprising at least two textile and/or metal cords. When cut to size, the latter is also termed “strip-like element”.
With the term “parameter”, it is intended a characteristic which can affect the quality of the tyre. The parameter is associated with one or more from among: starting components, steps for obtaining the semifinished products, semifinished products, steps for building the green tyre, green tyre, vulcanisation, moulded and vulcanised tyre. By way of example, in the case of elastomeric materials, a parameter is constituted for example by the relative expiry date. In the case of semifinished products and/or of the green tyre and/or of the moulded and vulcanised tyre, a parameter is constituted for example by the concentration and/or size of air bubbles. In the case of moulded and vulcanised tyres, a parameter is constituted for example by the presence and size of moulded cracks on the inner surface of the tyre or by the possible lack of material on the tread.
By “acceptable interval” relative to the value of a parameter, it is intended an interval of values that are acceptable or acceptable with reserve. The latter determine further controls relative to the element or step to which the parameter refers (for example, for the moulded and vulcanised tyre the presence or size of said cracks) in order to subsequently determine acceptance, auxiliary processing in order to attain acceptance or discard. By “discard interval” relative to the value of a parameter, it is intended an interval of values such to cause the discard of the element, of the step or of the element relative to a certain step to which the parameter refers. Preferably a discard threshold divides the acceptable interval from the discard interval.
With the term “detection system”, it is intended a preferably automatic inspection system adapted for detecting a specific parameter. With the term “automatic visual control”, it is intended a particular detection system defining a system for the automatic inspection of the moulded and vulcanised tyre.
With the term “actual resolution” of the detection system or of the automatic visual control, it is intended the resolution directly ascribable to the instrumentation that has improved due to the data processing capacity. With the term “control unit”, it is intended the logical set of one or more of the control units provided for in the plant.
With the term “succession of values”, it is intended a set of at least two values of a specific parameter. A particular example of succession is a time succession and/or a succession of values corresponding to one or more from among different: starting components, steps for obtaining the semifinished products, semifinished products, steps for building the green tyre, green tyre, vulcanisation, moulded and vulcanised tyre.
With the expression “controlling the trend” of the succession of values, it is intended controlling if the succession of values (or a function representative of the succession of the values) approaches or moves away from a threshold value (e.g. a discard threshold). More preferably “controlling the trend” can signify calculating the difference between each of the values of the succession and said threshold value (e.g. the value of a discard threshold) and controlling the progression thereof along said succession, indicating if it increases, decreases or remains constant in absolute terms. Possibly, “controlling the trend” can signify calculating the first derivative of the function representative of the succession of the values of the parameter and evaluating the sign thereof as a function of the value of said threshold (e.g. discard threshold) and of the values of the parameter, or evaluating the slope of the line joining two values of the parameter always as a function of the value of said threshold (e.g. discard threshold) and of the values of the parameter.